Articulated coupling arrangements used for the purpose of connecting adjacently disposed ends of a pair of railway freight cars together in a substantially semi-permanent fashion are well know in the art of railway freight vehicles. These articulated coupling arrangements have to accommodate the longitudinal travel in both directions, as well as the vertical and lateral travel at the coupling as the railway freight cars progress along the rails. The greater loads carried by modern railway cars necessitated articulated coupling arrangements which are capable of maintaining a close-butted relationship between various components to lessen the impact forces on railway cars and the articulated coupling arrangements. As a result, closed buttoned relationships lead to the development of slackless articulated coupling arrangements primarily consisting of couplers and drawbars. The term slackless means that the coupler or drawbar of a particular design is disposed within the center sill in a manner which minimizes longitudinal play or movement.
The main advantage of the coupler generally used with the draft gear assembly is that it accommodates the longitudinal travel in both directions, as well as the vertical and lateral travel at the coupling as the railway freight cars progress along the track and, more particularly, enabling such cars to more easily negotiate the curved portion of the track which will be encountered during operation. The primary disadvantage of the coupler is the play or slack in a longitudinal direction increasing the load forces onto a railway freight car. An additional disadvantage of the coupler and the draft gear assembly is the high unit costs due to the complexity of the design and a requirement for a significant number of the components.
Lately, the slackless drawbar assemblies have all but eliminated the need for a relatively expensive draft gear assembly used with coupler arrangements. Furthermore, these slackless drawbar assemblies have generally resulted in a desirable overall net decrease in the empty weight of such railway freight cars as well as in overall decrease in unit cost.
Each of the slackless drawbar assemblies which are known to be in use at the present time, however, suffer from at least one important and common disadvantage. This common disadvantage is that these slackless drawbar assemblies do not accommodate vertical and lateral travel at the coupling as the railway freight cars progress along the rails and, more particularly, while curving, thus increasing possibility of a flange climb derailment.
Additionally, the slackless drawbar may be employed to connect adjacently disposed ends of a pair of a railway freight cars with one car having worn wheels while the other cars have new wheels. Given this condition, the slackless drawbar will then be disposed at an angle in the vertical plane creating an additional vertical force onto a railway freight car having new wheels. This problem is especially magnified when the slackless drawbar is employed to connect adjacently disposed ends of a pair of aluminum lightweight construction coal carrying railway freight cars or an empty weight car. In this application, the slackless drawbar disposed at the angle in a vertical plane may cause the separation of the freight car body from the bolster or it may even cause lifting of the entire fright car from the rail.
As of particular significance is a reduction of frictional resistance to side loads to reduce side movement of the connecting adjacently disposed ends of a pair of railway cars and, more importantly, to reduce wheel and rail wear resulting from such side movement and to further minimize the possibility of a flange climb derailment.
As it can be seen from the above discussion it is desirable to employ a slackless drawbar which allows for vertical and lateral movement.
A common method of providing a slackless arrangement is to utilize a tapered gravity type wedge between a rear wall of a pocket casting (secured in the center sill) and a follower block which rests against the butt end of the coupler or drawbar member. The gravity wedge tends to force the follower block away from the pocket casting end wall and firmly against the butt end of the coupler or drawbar member shank. When component wear occurs subsequently increasing longitudinal clearances between the follower block and the coupler or drawbar member, the clearance or the slack is constantly being taken up by the action of the dropping gravity wedge.
In railway freight cars being pushed (buff), the longitudinal forces cause compression of the slackless coupler or drawbar member against the follower, gravity wedge and pocket end wall of the slackless arrangement.
When cars are being pulled (draft), the longitudinal forces tending to separate the slackless drawbar or coupler from the pocket end wall creating a condition where the gravity wedge can descend under gravity and lock when the railway freight cars are under the buff load.
With the above discussion in mind, attention is now directed to a particular prior art type gravity wedge for a slackless railcar connector assembly. This prior art gravity wedge is taught in U.S. Pat. No. 5,573,126. Disclosed therein is a tapered gravity wedge having a resilient means comprised of an elastomeric or a conventional compression spring disposed within a close tolerance machined bore on one or both faces of the gravity wedge and which protrudes slightly beyond one or both faces of the gravity wedge so that a small, but controlled gap symmetrically remains between the gravity wedge face(s) and the adjacent surface(s). When railcar buff loads are released, the only locked-in force operating on the connector assembly will be that dictated by the compressive load rate of the resilient means. When the buff or compressive load has been released, the gravity wedge will maintain its vertical position as the resilient means “feeds out” and holds the gravity wedge in place, until the next-experienced tensile loading.
One of the disadvantages of the gravity wedge of the prior art is the increased cost of the close tolerance machined bores. The other disadvantage is the impact of the environmental factors, such as temperature, humidity, dust and moisture affecting the structural integrity and operation of the resilient means thus enabling descend of the gravity wedge under a draft load condition.
Therefore, it is desirable to improve upon retainment of the gravity wedge.